The present invention relates to a locking device for vehicle safety seat belts of the type in which a strap of the seat belt is automatically retracted into a cover and wound onto a wind-up reel when the seat belt is not in use, for locking the reel when the strap in the seat belt is rapidly extended.
It is known in the prior art to provide locking of a reel in a safety seat belt retractor by using a locking member which is resting in a rotatable body, the body being attached to the reel and rotating with the reel, and which is movable in the rotatable body between an inner position (radially seen) and an outer position. In the inner position, free position, the locking member does not prevent rotation of the rotatable body, and in the outer position, locking position, the locking member engages with a fixed stop means mounted around the reel and prevents further rotation of the rotatable body, so that the reel is locked and further extension of the seat belt strap is prevented. In these devices the movement of the locking member is normally controlled by an inertia means which is pivotally mounted on the reel and which follows the rotatable body in its rotation when the strap is slowly extended from the reel. Due to its inertia, however, the inertia means is turned in relation to the rotatable body when the strap is rapidly extended, whereby the locking member is moved from the free position to the locking position. The inertia means is actuated by a spring, so that it normally keeps the locking member in the free position. Locking devices of this type are disclosed, for example, in the U.S. Pat. Nos. 3,442,467 and 3,770,225.
In locking devices of the type described above it is difficult to hold and control the locking member or locking members, as normally several locking members are used for locking the rotatable body, in a simple and reliable way. Therefore, the previously known locking devices are complicated in mechanical respect which means high manufacturing costs and frequently insufficient reliability in operation. In the device according to the U.S. Pat. No. 3,442,467 balls are used as locking members, and the balls are held and controlled between the locking position and the free position by a special member which is turned by an inertia means and which by means of extending tabs holds and controls the balls in notches in the rotatable body when locking and releasing, respectively, the body rotating with the reel. As the balls are moved in a radial direction when locking and releasing, respectively, it is difficult to provide with certainty holding and controlling functions in all positions by such a pivotally mounted means on the reel. In the device according to the U.S. Pat. No. 3,770,225 cylindrical rollers are used as locking members. These rollers are kept in slots in a cage member and are movable in radial direction by turning a pawl hub mounted in the cage member in relation to the cage member keeping the rollers. In this device the rollers are kept in their inner positions, free positions, by means of a spring ring surrounding the cage member. Thus, the spring force from the spring ring has to be overcome, when the rollers have to be moved to their locking positions. Also this device is complicated to manufacture and difficult to adjust.